The origin of the “local” ¼ keV X-ray flux

The Solar Wind interacts with interstellar neutrals via charge exchange producing a spatially and temporally varying x-ray flux difficult to separate from other diffuse sources. The Diffuse X-rays from the Local Galaxy (DXL) mission measured the spatial signature of Solar Wind Charge eXchange (SWCX) emission using 2 large-area proportional counters. DXL was able to separate the SWCX contribution from the more dominant flux originating in the Local Hot Bubble. The data from the mission provide a robust estimate of the SWCX contribution to the RASS data in the ¼ keV band, showing that the total SWCX contribution is 40%±5% (stat) ±5% (sys) of the minimal ¼ keV flux in the Galactic plane. This result implies that the measured fluxes are dominated by interstellar emission, strengthening the idea of a hot bubble filling the cavity in the local interstellar medium extending ~50-150 pc from the Sun. Combined with recent three-dimensional maps of the local interstellar medium and Voyager measurements of the magnetic field outside the heliosphere, it also leads to a consistent picture of the local interstellar environment.